Helpful?

https://www.youtube.com/watch?v=Bf1k9-4bb4w

Animation of refraction


https://phet.colorado.edu/en/simulation/bending-light

This one requires Java on your computer.

For Friday

Hi.

Let's be sure that we understand Snell's law.  With that in mind, answer the following questions:

1.  What is an index of refraction?

2.  What is Snell's law, and what do all of the symbols represent?

3.  Draw a picture that represents a light Ray hitting a piece of glass at an angle of 30 degrees with respect to a normal (perpendicular) line.

4.  In the problem above, if the light 

is refracted to an angle of 14 degrees, what is the index of refraction of the glass piece?  Light comes in from air.

5.  Now, a light Ray hits a new material with index of 1.8, at an angle of 45 degrees.  What is the angle of refraction inside the material?  

6.  What exactly is a critical angle?

Thank you.

HW for Wednesday

For next class, come with a definition of:

Total internal reflection and/or critical angle

If you have time, look into the concept/technology of fiber optics.

HW for Monday

Use your data from class to calculate the index of refraction for the clear block of acryllic.  Answers will probably be around 1.5.  If you have data for water, calculate the index of refraction for it as well; that will be around 1.3 or so.

Here are some problems to try.  Use the following:

n = c/v

Snell's law:  n1 sin(theta 1) = n2 sin(theta 2), to solve.


1.  What is the index of refraction for a substance that slows light down to half its speed in a vacuum?

(2)

2.  What is the index of refraction for a substance that takes an initial light ray in air at 50 degrees (with respect to a normal line) and bends it to 34 degrees?

(1.37)

3.  A light ray hits a block of plexiglass (n = 1.65) at 45 degrees.  What is the angle of refraction inside the block?

(25.5 degrees)

4.  Thought questions.  Why do you suppose triangular prisms "break up" light into colors of the rainbow?  Would the same thing happen if a red laser entered a triangular prism in the same way?  Are post-rain rainbows a similar phenomenon?

From Pink Floyd:

Trig HW for Thursday

Make sure your calculator is in degrees mode.  To check, hit the MODE button and look for the row (3rd down?) which reads "radian degree".  If "degrees" is not highlighted, scroll down to it and hit ENTER.  Then close MODE by hitting 2ND MODE.

Consider a 5-12-13 right triangle.

1.  Draw this.  Let the 5 side be horizontal (adjacent side).  13 is obviously the hypotenuse and 12 is the opposite side.

2.  So that we are on the same page, consider your reference angle as the angle between 5 and 13.

3.  Find the values for sin, cos and tan of the reference angle.

(12/13, 5/13, 12/5)

4.  Use the 2ND SIN function to find the angle itself.  (You could also use 2ND COS or 2ND TAN.)

2ND SIN (12/13) = 67.38 degrees

5.  Repeat this for an 8-15-17 triangle, if you have time.

FYI:  https://en.wikipedia.org/wiki/Pythagorean_triple



Part 2.  Calculator practice.  Find these:

1.  sin 0

(0)

2.  sin 30

(0.5)

3.  sin 45

(0.707)

4.  sin 60

(0.866)

5.  sin 90

(1)

6.  cos 0

(1)

7.  cos 45

(0.707)

8.  cos 60

(0.5)

9.  cos 90

(0)

Inverse practice.  Find the angle, knowing that:

1.  sin (theta) = 0.6

(36.9 degrees)

2.  sin (theta) = 0.25

(14.5 degrees)

3.  cos (theta) = 0.75

(41.4 degrees)

(If you've forgotten how to do these, recall the part about the 2ND SIN (or 2ND COS) functions.)

Probably the most important thing to remember here is what sine, cosine, and tangent actually represent -  they are RATIOS of sides associated with a particular angle.  For example, if a right triangle has a 30-degree angle in it, the sine of that angle (0.5) tells us that the ratio of the length of the side opposite that angle to the length of the hypotenuse is 0.5.

On the other hand, if we only knew the sine value (or cosine or tangent value), we could use that information to find the angle itself.  In the old days, you'd look up a value in a big chart.  Now, your calculator goes through an algorithm to solve for the angle.

For HW

Come to class with definitions of:

index of refraction

Snell's law

Also:

https://www.youtube.com/watch?v=EtsXgODHMWk

HW for Friday (11/6)

Comc to class with definitions of:

Reflection
Refraction
Dispersion
Diffraction

The answers should have something to do with light.